Searching for VHE gamma-ray emission associated with IceCube - PowerPoint PPT Presentation

Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos using FACT, H.E.S.S., MAGIC and VERITAS Marcos Santander*, Daniela Dorner, Jon Dumm, Konstancja Satalecka, Fabian Schüssler for the VERITAS, FACT, IceCube, MAGIC, and H.E.S.S. Collaborations * Barnard College - Columbia University 35 th International Cosmic Ray Conference Busan, South Korea — July 12-20, 2017

Multi-messenger search for cosmic-ray sources Spatial/Temporal correlations between neutrinos and gamma rays can trace cosmic-ray acceleration/interaction sites γ p + Astrophysical beam dump ν Galactic B-field p + p/ γ → X + π 0 → γγ → X + π + → µ + + ν µ µ + → e + + ν e + ¯ (oscillates to ~1:1:1) ν µ M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 2

IceCube astrophysical neutrinos IceCube combined spectrum IceCube Collab arxiv/1507.03991 Conventional atmospheric ( ν μ + ν e ) ∝ E − 2 . 50 ± 0 . 09 Astrophysical neutrino flux detected in the 20 TeV - 8 PeV energy range • Flux consistent with a power-law spectrum with spectral index in the 2.1 - 2.7 range. • Data compatible with flavor equipartition. • Event rate is low. ~ O (10) events / year. • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 3

IceCube astrophysical neutrinos 4-year HE Starting Event (HESE) sky map arxiv/1510.05223 For 6-year update see NU060 Sat 15 th (Claudio Kopper) No point-source detection. Distribution consistent with isotropy. • Point-source upper limits at the level of 1%-10% of the all-sky flux hint at large number • of sources (N > 10-100) . Search for VHE gamma-ray emission at the positions of likely-astrophysical neutrinos M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 4

Imaging Atmospheric Cherenkov Telescopes MAGIC H.E.S.S. VERITAS Southern Arizona (USA) Canary Islands (Spain) Khomas Highland (Namibia) Sensitive to VHE (E > 100 GeV) gamma-rays. Effective areas of ~ O (10 5 ) m 2 . ~0.1° angular • resolution. Used to observe the location of IceCube neutrino events to search for gamma-ray emission. • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 5

Gamma-ray FoVs and IceCube events 5° HESS-I FACT 4.5° “Cascade” events 15° CC ν e ν τ interactions, NC any flavor VERITAS 3.5° MAGIC Moon “Track” events HESS-II 3.2° CC ν µ interactions ~1° Only muon “track” events can be used in the follow-up observations given the IACTs’ field-of-view M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 6

Selection of IceCube track events for IACT follow-up Equatorial Coords Visible to FACT/MAGIC/VERITAS Visible to H.E.S.S. Galactic Plane GC High-energy muon neutrino events selected from three IceCube event samples: • HE starting events ( HESE , 13 tracks, arxiv/1510.05223). • HE through-going muon tracks, two years ( HEMU2 , 21 highest-energy events, arxiv/1507.04005). • HE through-going muon tracks, six years ( HEMU6 , 29 highest-energy events, arxiv/1607.08006). • Astrophysical probability for the events > 50%. • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 7

Summary of observations ID RA Dec Ang. res. H.E.S.S. obs. MAGIC obs. VERITAS obs. [ � ] [ � ] [ � ] time [min] time [min] time [min] HESE-05 110.6 -0.4 < 1 . 2 � 72 - 205 HESE-13 67.9 40.3 < 1 . 2 � - - 242 HESE-18 345.6 -24.8 < 1 . 3 � 486 - - HESE-37 167.3 20.7 < 1 . 2 � - 447 138 HESE-38 93.3 14.0 < 1 . 2 � - 342 90 HESE-44 336.7 0.0 < 1 . 2 � 432 - - HESE-45 219.0 -86.3 < 1 . 2 � 270 - - HEMU2-02 88.5 0.2 ∼ 1 � - - 133 HEMU2-03 37.1 18.6 ∼ 1 � - - 180 HEMU2-05 331.0 11.0 ∼ 1 � - - 60 HEMU2-06 346.8 24.0 ∼ 1 � - - 115 HEMU2-07 267.5 13.8 ∼ 1 � - - 25 HEMU2-08 238.3 18.9 ∼ 1 � - - 30 HEMU2-09 235.2 19.3 ∼ 1 � - - 30 HEMU2-11 323.3 2.8 ∼ 1 � - - 40 HEMU2-13 9.4 7.8 ∼ 1 � - - 115 HEMU2-14 207.2 6.7 ∼ 1 � - - 76 HEMU2-19 221.9 3.2 ∼ 1 � - - 20 HEMU2-20 138.9 47.6 ∼ 1 � - - 60 HEMU2-21 31.2 11.8 ∼ 1 � - - 60 HEMU6-20 169.61 28.04 < 0 . 5 � - - 50 HEMU6-27 110.63 11.42 < 0 . 3 � - 648 110 HEMU6-28 100.48 4.56 < 0 . 3 � - - 80 Total exposure 24.0 31.0 21.0 [hours] A global exposure of 76 hours has been collected by the three major IACTs. • Data sets are analyzed independently by each IACT group. • No VHE gamma-ray excess found in the region of interest of the neutrino events M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 8

Gamma-ray flux upper limits ULs from H.E.S.S. and VERITAS 68% range Full range IceCube 7-year PS discovery potential arXiv/1609.04981 0.1% of all-sky IceCube flux 3-year HESE arxiv/1405.5303 Differential upper limits (95% CL) are calculated at the central neutrino position for all • observations. Median ULs are calculated in 10 energy bins. For reference, the ULs are compared to the IceCube all-sky flux scaled by 10 -3 . • Only valid at the central neutrino position. • M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 9

Integral gamma-ray upper limit maps The neutrino angular uncertainty is • much larger than the IACT PSF. The IACT observations give us good • coverage of the 50% containment region of the neutrino events. We calculate integral upper limits • (95% CL) above an energy threshold for a E -2 spectrum on a regular grid. These ULs give constraints on any • gamma-ray excess or on potential nearby electromagnetic counterparts. M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 10

Integral gamma-ray upper limit maps The neutrino angular uncertainty is • much larger than the IACT PSF. 50% neutrino containment The IACT observations give us good • coverage of the 50% containment region of the neutrino events. We calculate integral upper limits • (95% CL) above an energy threshold for a E -2 spectrum on a regular grid. These ULs give constraints on any • gamma-ray excess or on potential nearby electromagnetic counterparts. 1° M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 10

Integral gamma-ray upper limit maps IACT pointings The neutrino angular uncertainty is • much larger than the IACT PSF. 50% neutrino containment The IACT observations give us good • coverage of the 50% containment region of the neutrino events. We calculate integral upper limits • (95% CL) above an energy threshold for a E -2 spectrum on a regular grid. These ULs give constraints on any • gamma-ray excess or on potential nearby electromagnetic counterparts. 1° M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 10

Integral gamma-ray upper limit maps IACT pointings The neutrino angular uncertainty is • much larger than the IACT PSF. 50% neutrino containment The IACT observations give us good • coverage of the 50% containment region of the neutrino events. We calculate integral upper limits • (95% CL) above an energy threshold for a E -2 spectrum on a regular grid. These ULs give constraints on any • gamma-ray excess or on potential nearby electromagnetic counterparts. 1° M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 10

Integral gamma-ray upper limit maps IACT pointings The neutrino angular uncertainty is • much larger than the IACT PSF. 50% neutrino containment The IACT observations give us good • coverage of the 50% containment region of the neutrino events. We calculate integral upper limits • (95% CL) above an energy threshold for a E -2 spectrum on a regular grid. These ULs give constraints on any • gamma-ray excess or on potential nearby electromagnetic counterparts. 1° M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 10

Integral gamma-ray upper limit maps IACT pointings The neutrino angular uncertainty is • much larger than the IACT PSF. 50% neutrino containment The IACT observations give us good • coverage of the 50% containment region of the neutrino events. We calculate integral upper limits • (95% CL) above an energy threshold for a E -2 spectrum on a regular grid. These ULs give constraints on any • gamma-ray excess or on potential nearby electromagnetic counterparts. 1° M. Santander - Searching for VHE gamma-ray emission associated with IceCube astrophysical neutrinos - ICRC 2017, Busan, Korea 10